A precise control method for wastewater denitrification based on active fermentation primary sedimentation system

Abstract

The present invention provides a precise control method for wastewater denitrification based on an activated fermentation primary sedimentation system, belonging to the field of environmental engineering technology. The high-efficiency activated fermentation primary sedimentation system provided by the present invention is achieved by modifying a traditional primary sedimentation tank by adding activated sludge return and a microaerobic aeration zone, effectively reducing investment and construction costs. Furthermore, based on this system, precise control of process operating parameters through microaerobic and activated fermentation, depending on the influent water quality and temperature, ensures efficient conversion of difficult-to-degrade organic matter in the influent of a sewage treatment plant, and achieves deep denitrification of wastewater without the addition of an external carbon source.

Description

Technical Field

[0001] The present invention belongs to the field of environmental engineering technology, and in particular relates to a precise control method for sewage denitrification based on an active fermentation primary sedimentation system, which is mainly used for the development of internal carbon sources in sewage treatment. Background Art

[0002] According to the "2022 Urban and Rural Construction Statistical Yearbook" of the Ministry of Housing and Urban-Rural Development, the scale of urban sewage treatment in my country has reached 216.06 million cubic meters per day, and the amount of dry sludge generated has reached 13.7 million tons per year. Urban sewage treatment mainly aims to remove nitrogen, phosphorus and organic matter. my country's urban sewage treatment mainly uses the activated sludge process, and the denitrifying functional microorganisms are mostly heterotrophic bacteria. Due to the low carbon-nitrogen ratio of the influent, it is usually necessary to add a carbon source during the denitrification stage to ensure the denitrification activity of the denitrifying functional bacteria so that the effluent water quality meets the total nitrogen emission standards. As the effluent water quality standards of sewage treatment plants continue to improve, it is conservatively estimated that the amount of carbon source added for denitrification in my country's sewage treatment exceeds 7.66 million tons per year, which not only significantly increases the cost of sewage treatment, but also increases indirect carbon emissions. The "Implementation Opinions on Promoting Synergistic Efficiency Improvement in Pollution Reduction and Carbon Reduction in Wastewater Treatment" jointly issued by the National Development and Reform Commission, the Ministry of Housing and Urban-Rural Development and other departments requires the coordinated promotion of pollutant reduction and greenhouse gas emission reduction in the entire wastewater treatment process, the implementation of water conservation and efficiency improvement at the source, energy conservation and carbon reduction in the treatment process, and resource utilization of sewage sludge, to comprehensively improve the comprehensive efficiency of wastewater treatment and create a green and low-carbon benchmark wastewater treatment plant with efficient recycling of energy resources.

[0003] Organic matter in sewage is divided into biodegradable organic matter and refractory organic matter. Biodegradable organic matter mainly includes soluble proteins, polysaccharides, volatile fatty acids, etc., which can be directly utilized by denitrifying microorganisms to accelerate the denitrification reaction rate; refractory organic matter includes insoluble macromolecules such as large molecular proteins, long-chain fatty acids, and aromatic compounds, which cannot be directly utilized by denitrifying microorganisms. Therefore, making full use of the refractory organic matter in sewage and efficiently converting it into small molecular organic matter such as volatile fatty acids (VFA) and glucose, thereby achieving efficient denitrification without the need for additional chemical carbon sources, will effectively reduce the cost of denitrification in sewage treatment and reduce indirect carbon emissions.

[0004] Under the severe situation of global climate change, converting the difficult-to-degrade organic matter in sewage as a denitrification carbon source and achieving deep denitrification of low carbon-nitrogen ratio sewage without an external carbon source is of great significance for building a resource-saving and environmentally friendly society and achieving sustainable development. Summary of the Invention

[0005] The present invention provides a precise control method for sewage denitrification based on an active fermentation primary sedimentation system. The method precisely controls process operating parameters through microaerobic and active fermentation according to the influent water quality and water temperature, thereby ensuring the efficient conversion of difficult-to-degrade organic matter in the influent of the sewage treatment plant and achieving deep denitrification treatment of sewage without an external carbon source.

[0006] In order to achieve the above-mentioned objectives, the present invention provides a precise control method for sewage denitrification based on an active fermentation primary sedimentation system. The active fermentation primary sedimentation system is arranged before a conventional biological tank and a secondary sedimentation tank, and includes a primary sedimentation tank, an online monitoring instrument, an aeration system / pipeline and an activated sludge return pipeline. Based on the inlet temperature and COD concentration in the primary sedimentation tank, the activated sludge return ratio, sludge discharge volume and microaerobic ventilation ratio in the primary sedimentation tank are precisely controlled to achieve deep denitrification of low carbon-nitrogen ratio sewage without an external carbon source.

[0007] It is understandable that the high-efficiency active fermentation primary sedimentation system provided by the present invention adds activated sludge return and micro-aerobic aeration zone on the basis of conventional horizontal flow primary sedimentation tanks. According to the inlet water temperature and COD concentration, the activated sludge return ratio, sludge discharge volume, micro-aerobic ventilation ratio and other process operating parameters are accurately controlled, and deep denitrification of low carbon-nitrogen ratio sewage without an external carbon source can be achieved. Among them, by returning the activated sludge and providing a micro-aerobic environment, the types of hydrolysis and acidification functional microorganisms in the primary sedimentation tank can be enriched, the abundance and activity of key microbial populations can be improved, and the difficult-to-degrade large-molecule organic matter in the sewage and primary sedimentation tank sludge can be quickly hydrolyzed to produce small-molecule organic matter that is easily utilized by denitrification functional microorganisms, which can increase the concentration of dissolved organic matter and volatile fatty acids in the inlet water of the subsequent biological treatment system, thereby achieving deep denitrification of low carbon-nitrogen ratio sewage without an external carbon source.

[0008] Preferably, the activated sludge in the primary sedimentation tank is returned from the biological or secondary sedimentation tank. The activated sludge is returned to the primary sedimentation tank's inlet pipe to be thoroughly mixed with the influent. It is understood that activated sludge consists of organic matter, inorganic matter, and attached microorganisms. The industry refers to the sludge from biological and secondary sedimentation tanks as activated sludge. Primary sedimentation tanks typically contain very few microorganisms, and their sludge is primarily composed of organic and inorganic matter, thus becoming primary sludge.

[0009] Preferably, a variable frequency pump and a flow meter are respectively provided on the activated sludge return pipe of the biological tank or the secondary sedimentation tank to control the sludge flow rate of the activated sludge returning to the primary sedimentation tank.

[0010] Preferably, a COD and temperature online monitoring instrument is provided on the water inlet pipe of the primary sedimentation tank to monitor the COD concentration and temperature of the inlet water;

[0011] An online sludge concentration monitoring instrument, a variable frequency pump and a flow meter are installed at the bottom of the primary sedimentation tank to control the sludge concentration at the bottom of the primary sedimentation tank.

[0012] Preferably, the primary sedimentation tank includes a micro-aerobic aeration zone, which is an area at the bottom of the primary sedimentation tank where a perforated or microporous aeration system / pipeline is arranged, and the area is from the water inlet to the 15% to 50% area, preferably the 25% to 35% area;

[0013] The perforated or microporous aeration system / pipeline is equipped with an air flow meter and a blower valve, and the aeration volume at the bottom of the primary sedimentation tank is controlled by adjusting the valve opening.

[0014] Preferably, the hydraulic retention time of the high-efficiency active fermentation primary sedimentation system is 1.5 to 3.5 hours, preferably 2.5 hours.

[0015] As a preferred method, according to the inlet water temperature and COD concentration in the primary sedimentation tank of the primary sedimentation system, the activated sludge return ratio, sludge discharge volume and microaerobic ventilation ratio in the primary sedimentation tank are precisely controlled to achieve deep denitrification of low carbon-nitrogen ratio sewage without adding an external carbon source. Specifically, the method includes:

[0016] When the inlet water temperature T is less than or equal to 10°C, the activated sludge return ratio W is controlled to be 1+(C-500) / (C+500)×5%. The frequency conversion pump of the biological tank or secondary sedimentation tank and the flow meter of the activated sludge return pipe are used to adjust the pump operating frequency to control the flow rate of the activated sludge return to the primary sedimentation tank to be Q×W. The microaerobic zone ventilation ratio A is controlled to be 1+(C-500) / (C+500)×0.35. The aeration volume at the bottom of the primary sedimentation tank is controlled to be V×A×R by adjusting the blower valve opening in combination with the air flow meter on the microporous aeration system / pipeline. The bottom sludge concentration is controlled to be 18,000-19,000 mg / L. When the sludge concentration is greater than 19,000 mg / L, the sludge discharge volume is increased, and when the sludge concentration is less than 18,000 mg / L, the sludge discharge volume is reduced.

[0017] When the inlet water temperature T is less than 10°C and is less than or equal to 15°C, the activated sludge return ratio W is controlled to be 4.5% (1+(C-500) / (C+500)). The frequency of the variable frequency pump in the biological tank or secondary sedimentation tank and the flow meter in the activated sludge return pipe are used to adjust the pump operating frequency to control the flow rate of the activated sludge returned to the primary sedimentation tank to be Q×W. The aeration ratio in the microaerobic zone is controlled to be A (1+(C-500) / (C+500)). The air flow rate at the bottom of the primary sedimentation tank is controlled to be V×A×R by adjusting the blower valve opening in combination with the air flow meter on the microporous aeration system / pipeline. The bottom sludge concentration is controlled to be 17,500-18,500 mg / L. When the sludge concentration is greater than 18,500 mg / L, the sludge discharge rate is increased, and when the sludge concentration is less than 17,500 mg / L, the sludge discharge rate is reduced.

[0018] When the inlet temperature T is 15°C < ≤ 20°C, the activated sludge return ratio W is controlled to be 1+(C-500) / (C+500) × 4%. The frequency conversion pump of the biological tank or secondary sedimentation tank and the flow meter of the activated sludge return pipe are used to adjust the pump operating frequency to control the flow rate of the activated sludge return to the primary sedimentation tank to be Q×W. The microaerobic zone ventilation ratio A is controlled to be 1+(C-500) / (C+500) × 0.25. The aeration volume at the bottom of the primary sedimentation tank is controlled to be V×A×R by adjusting the blower valve opening in combination with the air flow meter on the microporous aeration system / pipeline. The bottom sludge concentration is controlled to be 17,000-18,000 mg / L. When the sludge concentration is greater than 18,000 mg / L, the sludge discharge volume is increased, and when the sludge concentration is less than 17,000 mg / L, the sludge discharge volume is reduced.

[0019] When the inlet temperature T is 20°C < ≤ 25°C, the activated sludge return ratio W is controlled to be 〔1+(C-500) / (C+500)〕×3.5%. The frequency conversion pump of the biological tank or secondary sedimentation tank and the flow meter of the activated sludge return pipe are used to adjust the pump operating frequency to control the flow rate of the activated sludge return to the primary sedimentation tank to be Q×W. The microaerobic zone ventilation ratio A is controlled to be =(1+(C-500) / (C+500))×0.2. The air flow rate at the bottom of the primary sedimentation tank is controlled to be V×A×R by adjusting the blower valve opening in combination with the air flow meter on the microporous aeration system / pipeline. The bottom sludge concentration is controlled to be 16500-17500 mg / L. When the sludge concentration is greater than 17500 mg / L, the sludge discharge volume is increased, and when the sludge concentration is less than 16500 mg / L, the sludge discharge volume is reduced.

[0020] When the inlet water temperature T is greater than 25°C, the activated sludge return ratio W is controlled to be [1+(C-500) / (C+500)] × 3%. The frequency conversion pump of the biological tank or secondary sedimentation tank and the flow meter of the activated sludge return pipe are used to adjust the pump operating frequency to control the flow rate of the activated sludge returned to the primary sedimentation tank to be Q×W. The microaerobic zone ventilation ratio A is controlled to be (1+(C-500) / (C+500)) × 0.15. The air flow rate at the bottom of the primary sedimentation tank is controlled to be V×A×R by adjusting the blower valve opening in combination with the air flow meter on the microporous aeration system / pipeline. The bottom sludge concentration is controlled to be 16,000-17,000 mg / L. When the sludge concentration is greater than 17,000 mg / L, the sludge discharge volume is increased, and when the sludge concentration is less than 16,000 mg / L, the sludge discharge volume is reduced.

[0021] Where C represents the influent COD concentration, in mg / L; Q represents the influent flow rate of the primary sedimentation tank, in m 3 / h; V represents the volume of the primary sedimentation tank, unit is m 3 ; R represents the proportion of the aeration area at the bottom of the primary sedimentation tank; the ventilation ratio is the ratio of the ventilation volume per minute to the sewage volume, unit is vvm.

[0022] Preferably, the carbon-nitrogen ratio in the low carbon-nitrogen ratio sewage is less than 3:1.

[0023] Preferably, the concentration of dissolved organic matter in the influent is increased by 20-35%, and the concentration of volatile fatty acids (VFA) is increased by 10-30%.

[0024] Compared with the prior art, the advantages and positive effects of the present invention are:

[0025] The high-efficiency active fermentation primary sedimentation system provided by the present invention is obtained by adding activated sludge return and micro-aerobic aeration zone to the traditional primary sedimentation tank, which can effectively reduce investment and construction costs. On this basis, according to the influent water quality and water temperature, the process operation parameters are accurately controlled through micro-aerobic and active fermentation, which can ensure the efficient conversion of difficult-to-degrade organic matter in the influent of the sewage treatment plant, and can increase the dissolved organic matter concentration of the influent of the sewage treatment plant biological pool by 20-35%, and increase the volatile fatty acid (VFA) concentration by 10-30%. On the basis of achieving deep denitrification of sewage treatment without adding an external carbon source, the operating cost is further reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of a high-efficiency active fermentation primary sedimentation system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0028] Example 1

[0029] The urban sewage treatment plant in a coastal city in northern China has a treatment capacity of 50,000 cubic meters per day. The biological treatment unit adopts a three-stage AO+MBBR process (aerobic-anaerobic+moving bed biofilm reactor process). The high-efficiency active fermentation primary sedimentation system is based on the transformation of the original horizontal flow sedimentation tank. The activated sludge comes from the activated sludge return of the secondary sedimentation tank and flows back to the water inlet pipe of the primary sedimentation tank; the biological tank (3) (the biological tank is the largest structure in the sewage treatment process, and its volume is usually about 10 times that of the primary sedimentation tank and the secondary sedimentation tank. Figure 1In order to highlight the technical features of the primary sedimentation tank, the size is shown schematically here) or the activated sludge return pipe (12) of the secondary sedimentation tank (4) is respectively provided with a variable frequency pump (6) and a flow meter (5) to control the sludge flow of the activated sludge returning to the primary sedimentation tank (2); the water inlet pipe (1) of the primary sedimentation tank is provided with a COD online monitoring instrument (7) and a temperature online monitoring instrument (11) to monitor the COD concentration and temperature of the influent; the bottom of the primary sedimentation tank is provided with a sludge concentration online monitoring instrument (13), a flow meter (14) and a variable frequency pump (not shown) to control the sludge concentration at the bottom of the primary sedimentation tank. The high-efficiency active fermentation primary sedimentation system is provided with a microporous aeration device (10) at the bottom of the area from the water inlet to 30%, the hydraulic retention time is 2.5h, and the primary sedimentation tank capacity is 5200m 3 .

[0030] The COD concentration of the influent of the high-efficiency active fermentation primary sedimentation system is monitored by online monitoring instruments, which is C (unit: mg / L) and the water temperature T (unit: °C). The influent flow rate Q of the primary sedimentation tank is 2000-2200m 3 / h, the volume of the primary sedimentation tank V is 5000m 3 , according to the influent water quality and water temperature, determine the process operating parameters according to the following settings:

[0031] When T≤10, the activated sludge return ratio W=〔1+(C-500) / (C+500)〕×5%, the frequency conversion pump (6) of the biological pool or secondary sedimentation tank and the flow meter (5) of the activated sludge return pipe are used to adjust the pump operating frequency and control the flow rate of the activated sludge returning to the primary sedimentation tank to Q×W; the micro-aerobic zone ventilation ratio A=〔1+(C-500) / (C+500)〕×0.35, combined with the microporous aeration system / pipeline (10) on The air flow meter (not shown) controls the aeration volume at the bottom of the primary sedimentation tank to be 5200×A×30% by adjusting the opening of the valve (not shown) of the blower (8); controls the bottom sludge concentration to be 18000-19000 mg / L, and controls the bottom sludge concentration by the sludge discharge volume of the primary sedimentation tank. When the sludge concentration is greater than 19000 mg / L, the sludge discharge volume is increased by the sludge discharge pump (9), and when the sludge concentration is less than 18000 mg / L, the sludge discharge volume is reduced.

[0032] When 10 < T ≤ 15, control the return ratio of activated sludge W = [1 + (C - 500) / (C + 500)] × 4.5%. Through the variable-frequency pump in the biological tank or secondary sedimentation tank and the flowmeter in the activated sludge return pipeline, adjust the pump operation frequency to control the flow rate of activated sludge returning to the primary sedimentation tank as Q × W; control the aeration ratio A in the micro-aerobic zone = [1 + (C - 500) / (C + 500)] × 0.3. Combining with the air flowmeter on the microporous aeration system / pipeline, adjust the opening of the blower valve to control the aeration volume at the bottom of the primary sedimentation tank as 5200 × A × 30%; control the bottom sludge concentration at 17500 - 18500 mg / L. Control the bottom sludge concentration through the sludge discharge volume of the primary sedimentation tank. When the sludge concentration is greater than 18500 mg / L, increase the sludge discharge volume; when the sludge concentration is less than 17500 mg / L, decrease the sludge discharge volume.

[0033] When 15 < T ≤ 20, control the return ratio of activated sludge W = [1 + (C - 500) / (C + 500)] × 4%. Through the variable-frequency pump in the biological tank or secondary sedimentation tank and the flowmeter in the activated sludge return pipeline, adjust the pump operation frequency to control the flow rate of activated sludge returning to the primary sedimentation tank as Q × W; control the aeration ratio A in the micro-aerobic zone = [1 + (C - 500) / (C + 500)] × 0.25. Combining with the air flowmeter on the microporous aeration system / pipeline, adjust the opening of the blower valve to control the aeration volume at the bottom of the primary sedimentation tank as 5200 × A × 30%; control the bottom sludge concentration at 17000 - 18000 mg / L. Control the bottom sludge concentration through the sludge discharge volume of the primary sedimentation tank. When the sludge concentration is greater than 18000 mg / L, increase the sludge discharge volume; when the sludge concentration is less than 17000 mg / L, decrease the sludge discharge volume.

[0034] When 20 < T ≤ 25, control the return ratio of activated sludge W = [1 + (C - 500) / (C + 500)] × 3.5%. Through the variable-frequency pump in the biological tank or secondary sedimentation tank and the flowmeter in the activated sludge return pipeline, adjust the pump operation frequency to control the flow rate of activated sludge returning to the primary sedimentation tank as Q × W; control the aeration ratio A in the micro-aerobic zone = [1 + (C - 500) / (C + 500)] × 0.2. Combining with the air flowmeter on the microporous aeration system / pipeline, adjust the opening of the blower valve to control the aeration volume at the bottom of the primary sedimentation tank as 5200 × A × 30%; control the bottom sludge concentration at 16500 - 17500 mg / L. Control the bottom sludge concentration through the sludge discharge volume of the primary sedimentation tank. When the sludge concentration is greater than 17500 mg / L, increase the sludge discharge volume; when the sludge concentration is less than 16500 mg / L, decrease the sludge discharge volume.

[0035] When T>25, the activated sludge return ratio W is controlled to be 〔1+(C-500) / (C+500)〕×3%. The pump operating frequency of the biological tank or secondary sedimentation tank and the flow meter of the activated sludge return pipe are adjusted to control the flow rate of the activated sludge returning to the primary sedimentation tank to be Q×W. The microaerobic zone ventilation ratio A is controlled to be 〔1+(C-500) / (C+500)〕×0.15. The aeration volume at the bottom of the primary sedimentation tank is controlled to be 5200×A×30% by adjusting the blower valve opening in combination with the air flow meter on the microporous aeration system / pipeline. The bottom sludge concentration is controlled to be 16000-17000 mg / L by controlling the bottom sludge concentration through the sludge discharge volume of the primary sedimentation tank. When the sludge concentration is greater than 17000 mg / L, the sludge discharge volume is increased, and when the sludge concentration is less than 16000 mg / L, the sludge discharge volume is reduced.

[0036] For example, the inlet water temperature of the sedimentation tank was 22.5℃, the COD concentration was 523mg / L, the total nitrogen was 73mg / L, and the inlet flow rate was 2100m 3 / h, then the activated sludge return ratio W = [1 + (523-500) / (523 + 500)] × 3.5% = 3.58%. Through the frequency conversion pump of the biological pool or secondary sedimentation tank and the flow meter of the activated sludge return pipeline, the pump operating frequency is adjusted to control the flow rate of the activated sludge returning to the primary sedimentation tank to be Q × W = 2100 × 3.58% = 75.15m 3 / h; control the ventilation ratio of the microaerobic zone A = [1 + (523-500) / (523 + 500)] × 0.2 = 0.204, and adjust the blower valve opening by combining the air flow meter on the microporous aeration system / pipeline to control the aeration volume at the bottom of the primary sedimentation tank to 5200 × 0.204 × 30% = 318m 3 / h; the bottom sludge concentration is controlled at 16,500-17,500 mg / L. This is controlled by the discharge rate from the primary sedimentation tank. When the sludge concentration exceeds 17,500 mg / L, the discharge rate is increased; when the sludge concentration is less than 16,500 mg / L, the discharge rate is reduced. After the active fermentation primary sedimentation system, the dissolved organic matter in the influent increased from 127.5 mg / L to 151.2 mg / L, an average increase of approximately 18.6%. VFA increased from 40.3 mg / L to 58.8 mg / L, an increase of approximately 45.9%. Deep denitrification is achieved without the addition of an external carbon source, with the total nitrogen in the sewage treatment plant effluent at 8.5 mg / L.

[0037] The inlet water temperature of the primary sedimentation tank is 17.0℃, the COD concentration is 475mg / L, the total nitrogen is 82mg / L, and the inlet flow rate is 2050m 3 / h, then the activated sludge return ratio W = [1 + (475-500) / (475 + 500)] × 4% = 3.90%. Through the frequency conversion pump of the biological pool or secondary sedimentation tank and the flow meter of the activated sludge return pipeline, the pump operating frequency is adjusted to control the flow rate of the activated sludge returning to the primary sedimentation tank to be Q × W = 2050 × 3.90% = 79.90m 3 / h; control the ventilation ratio of the microaerobic zone A = [1 + (475-500) / (475 + 500)] × 0.25 = 0.244, and adjust the blower valve opening by combining the air flow meter on the microporous aeration system / pipeline to control the aeration volume at the bottom of the primary sedimentation tank to 5200 × 0.244 × 30% = 381m 3 / h; the bottom sludge concentration is controlled at 17,000-18,000 mg / L. This is controlled by the discharge rate from the primary sedimentation tank. When the sludge concentration exceeds 18,000 mg / L, the discharge rate is increased, and when the sludge concentration is less than 17,000 mg / L, the discharge rate is reduced. After the active fermentation primary sedimentation system, the dissolved organic matter in the influent increased from 119.6 mg / L to 143.5 mg / L, an average increase of approximately 20.0%. VFA increased from 38.4 mg / L to 53.2 mg / L, an increase of approximately 38.5%. Deep denitrification is achieved in wastewater treatment without the addition of an external carbon source, with the total nitrogen in the wastewater treatment plant effluent reaching 11.2 mg / L.

[0038] The inlet water temperature of the primary sedimentation tank is 9.2℃, the COD concentration is 567mg / L, the total nitrogen is 85mg / L, and the inlet flow rate is 2120m 3 / h, then the activated sludge return ratio W = [1 + (567-500) / (567 + 500)] × 5% = 5.31%. Through the frequency conversion pump of the biological pool or secondary sedimentation tank and the flow meter of the activated sludge return pipeline, the pump operating frequency is adjusted to control the flow rate of the activated sludge returning to the primary sedimentation tank to be Q × W = 2120 × 5.31% = 112.57m 3 / h; control the ventilation ratio of the microaerobic zone A = [1 + (567-500) / (567 + 500)] × 0.35 = 0.372, and adjust the blower valve opening by combining the air flow meter on the microporous aeration system / pipeline to control the aeration volume at the bottom of the primary sedimentation tank to 5200 × 0.372 × 30% = 580m 3 / h; the bottom sludge concentration is controlled at 18,000-19,000 mg / L. This is controlled by the discharge rate from the primary sedimentation tank. When the sludge concentration exceeds 19,000 mg / L, the discharge rate is increased, and when the sludge concentration is less than 18,000 mg / L, the discharge rate is reduced. After the active fermentation primary sedimentation system, the dissolved organic matter in the influent increased from 145.3 mg / L to 175.8 mg / L, an average increase of approximately 21.0%. VFA increased from 50.1 mg / L to 73.2 mg / L, an increase of approximately 46.1%. Deep denitrification is achieved in wastewater treatment without the addition of an external carbon source, with the total nitrogen in the wastewater treatment plant effluent reaching 13.5 mg / L.

[0039] After one year of continuous operation, the influent COD concentration varied from 300-700 mg / L, the influent total nitrogen concentration from 70-120 mg / L, and the influent temperature from 9-25°C, depending on seasonal variations. After the active fermentation primary sedimentation system, the dissolved organic matter in the influent increased from an average of 135.2 mg / L (annual average) to an average of 158.6 mg / L (annual average), an average increase of approximately 17.3%. VFA increased from an average of 45.1 mg / L to an average of 71.3 mg / L, an average increase of approximately 58.1%. Deep denitrification was achieved without the addition of an external carbon source, with the average total nitrogen in the sewage treatment plant's effluent being 12.7 mg / L.

Claims

1. A precise control method for wastewater denitrification based on an active fermentation primary sedimentation system, characterized in that: The active fermentation primary sedimentation system is installed before the conventional biological tank and secondary sedimentation tank, and includes the primary sedimentation tank, online monitoring instrumentation, aeration system / pipeline, and activated sludge return pipeline. Based on the inlet temperature and COD concentration in the primary sedimentation tank, the activated sludge return ratio, sludge discharge volume, and microaerobic ventilation ratio in the primary sedimentation tank are precisely controlled to achieve deep denitrification of low carbon-nitrogen ratio wastewater without the addition of an external carbon source. The primary sedimentation tank includes a micro-aerobic aeration zone, which is the area at the bottom of the primary sedimentation tank where the microporous aeration system / pipeline is laid out. The area is from the water inlet to the 15% to 50% area; The microporous aeration system / pipeline is equipped with an air flow meter and a blower valve. The aeration volume at the bottom of the primary sedimentation tank is controlled by adjusting the valve opening. Specifically include: When the inlet water temperature T is ≤ 10°C, the activated sludge return ratio W is controlled at 〔1+(C-500) / (C+500)〕×5%. The frequency of the variable frequency pump in the biological tank or secondary sedimentation tank and the flow meter in the activated sludge return pipe are used to adjust the pump operating frequency to control the flow rate of activated sludge returned to the primary sedimentation tank to Q×W. The aeration ratio of the microaerobic zone is controlled at 〔1+(C-500) / (C+500)〕×0.

35. The aeration volume at the bottom of the primary sedimentation tank is controlled at V×A×R by adjusting the blower valve opening in combination with the air flow meter on the microporous aeration system / pipeline. The bottom sludge concentration is controlled at 18,000-19,000 mg / L. When the sludge concentration is greater than 19,000 mg / L, the sludge discharge volume is increased, and when the sludge concentration is less than 18,000 mg / L, the sludge discharge volume is reduced. When the inlet water temperature T is less than 10°C and less than or equal to 15°C, the activated sludge return ratio W is controlled at 4.5% (1+(C-500) / (C+500)). The frequency of the variable frequency pump in the biological tank or secondary sedimentation tank and the flow meter in the activated sludge return pipe are used to adjust the pump operating frequency to control the flow rate of activated sludge returning to the primary sedimentation tank to Q×W. The aeration ratio in the microaerobic zone is controlled at A=0.3 (1+(C-500) / (C+500)). The air flow meter on the microporous aeration system / pipeline is used to adjust the blower valve opening to control the aeration volume at the bottom of the primary sedimentation tank to V×A×R. The bottom sludge concentration is controlled at 17,500-18,500 mg / L. When the sludge concentration is greater than 18,500 mg / L, the sludge discharge volume is increased, and when the sludge concentration is less than 17,500 mg / L, the sludge discharge volume is reduced. When the inlet temperature T is 15°C < ≤ 20°C, control the activated sludge return ratio W = [1 + (C-500) / (C+500)] × 4%. Adjust the pump operating frequency of the biological tank or secondary sedimentation tank and the flow meter on the activated sludge return pipe to control the flow rate of activated sludge returning to the primary sedimentation tank to Q × W. Control the microaerobic zone ventilation ratio A = [1 + (C-500) / (C+500)] × 0.

25. Combined with the air flow meter on the microporous aeration system / pipeline, adjust the blower valve opening to control the aeration volume at the bottom of the primary sedimentation tank to V × A × R. Control the bottom sludge concentration to 17,000-18,000 mg / L. When the sludge concentration is greater than 18,000 mg / L, increase the sludge discharge volume. When the sludge concentration is less than 17,000 mg / L, reduce the sludge discharge volume. When the inlet water temperature T is 20°C < ≤ 25°C, control the activated sludge return ratio W = [1 + (C-500) / (C+500)] × 3.5%. Adjust the pump operating frequency of the biological tank or secondary sedimentation tank and the flow meter on the activated sludge return pipe to control the flow rate of activated sludge returning to the primary sedimentation tank to Q × W. Control the microaerobic zone ventilation ratio A = (1 + (C-500) / (C+500)) × 0.

2. Combined with the air flow meter on the microporous aeration system / pipeline, adjust the blower valve opening to control the aeration volume at the bottom of the primary sedimentation tank to V × A × R. Control the bottom sludge concentration to 16,500-17,500 mg / L. When the sludge concentration is greater than 17,500 mg / L, increase the sludge discharge volume; when the sludge concentration is less than 16,500 mg / L, reduce the sludge discharge volume. When the inlet water temperature T is greater than 25°C, the activated sludge return ratio W is controlled at [1+(C-500) / (C+500)] × 3%. The frequency converter pump in the biological tank or secondary sedimentation tank and the flow meter in the activated sludge return pipe are used to adjust the pump operating frequency to control the flow rate of activated sludge returning to the primary sedimentation tank to Q × W. The microaerobic zone aeration ratio A is controlled at [1+(C-500) / (C+500)] × 0.

15. The aeration volume at the bottom of the primary sedimentation tank is controlled at V × A by adjusting the blower valve opening in combination with the air flow meter on the microporous aeration system / pipeline. The bottom sludge concentration is controlled at 16,000-17,000 mg / L. When the sludge concentration is greater than 17,000 mg / L, the sludge discharge volume is increased; when the sludge concentration is less than 16,000 mg / L, the sludge discharge volume is reduced. Where C represents the influent COD concentration, in mg / L; Q represents the influent flow rate of the primary sedimentation tank, in m 3 / h; V represents the volume of the primary sedimentation tank, unit is m 3 ; R represents the proportion of the aeration area at the bottom of the primary sedimentation tank; the ventilation ratio is the ratio of the ventilation volume per minute to the sewage volume, unit vvm; Based on the above method, the concentration of dissolved organic matter in the influent can be increased by 20-35%, and the concentration of volatile fatty acids (VFA) can be increased by 10-30%. The activated sludge in the primary sedimentation tank comes from the activated sludge return from the biological tank or the secondary sedimentation tank. The activated sludge is returned to the water inlet pipe of the primary sedimentation tank to be fully mixed with the inlet water.

2. The precise control method according to claim 1, characterized in that: The activated sludge return pipes of the biological tank or secondary sedimentation tank are respectively provided with a variable frequency pump and a flow meter to control the sludge flow rate of the activated sludge returning to the primary sedimentation tank.

3. The precise control method according to claim 1, characterized in that: The inlet pipe of the primary sedimentation tank is equipped with COD and temperature online monitoring instruments to monitor the COD concentration and temperature of the inlet water; An online sludge concentration monitoring instrument, a variable frequency pump and a flow meter are installed at the bottom of the primary sedimentation tank to control the sludge concentration at the bottom of the primary sedimentation tank.

4. The precise control method according to any one of claims 1 to 3, characterized in that: The hydraulic retention time of the high-efficiency active fermentation primary sedimentation system is 1.5~3.5h.

5. The precise control method according to claim 1, characterized in that: The carbon-nitrogen ratio in low-carbon-nitrogen ratio sewage is less than 3:1.

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